1. Field of the Invention
This invention relates to data processing systems. Data entered from a keyboard or other device is stored and continuously retrieved for display refreshing.
2. Description of the Prior Art
Terminal systems in today's data processing industry require remote terminals providing a keyboard for entering data, and a display for displaying data entered at the keyboard or communicated to the terminal from a remote processor or other terminal.
The functions provided and the cost of such terminals often determines their success in the marketplace, and that cost/function ratio is critically determined by the complexity and quantity of the logic components.
Various keyboard functions, such as N key lockout, two key rollover, and trailing and leading edge debounce are known in the prior art; as are display functions including the right justification of entered data, with the most recently entered character displayed at the rightmost position.
The prior art circuitry for providing these functions includes integrators on the key contacts for bounce protection, shift registers for providing key rollover protection, other shift registers for display refresh, and so forth.
The art is in need, therefore, of a simple circuit providing a wide range of keyboard protection features and display power-- which is efficient of hardware and which is, therefore, capable of packaging on a single integrated circuit chip to achieve optimum cost.